In the photographic art color images are formed by exposing a light sensitive silver halide photographic element to actinic radiation, followed by processing in which an oxidized aromatic primary amine color developing agent is reacted with a dye-forming coupler to form yellow, magenta and cyan image dyes in the element.
Among the known magenta dye-forming couplers are cyclic azoles such as pyrazolobenzimidazoles, pyrazolotriazoles, and imidazopyrazoles. More recently, some cyclic azoles have been described as cyan dye-forming couplers. Representative patents include U.S. Pat. Nos. 3,725,067, 4,540,654, 4,728,598, 4,873,183, 4,882,266, 4,916,051 and 5,206,130.
Dye-forming couplers in photographic elements should have good coupling efficiency and lead to dyes having desired hues. Coupling efficiency refers to how well the coupler reacts with oxidized silver halide developing agent to form dye under actual processing conditions. The larger the amount of dye produced per unit developed silver during the common processing time, other things being equal, the more efficient the coupler.
While many known cyclic azole couplers have desired hues, many do not have as good coupling efficiency as would be desirable. Thus, it would be desirable to have azole couplers with improved coupling efficiency.
Couplers which contain saccharin groups are known from U.S. Pat. Nos. 4,540,654, 4,585,732 and 5,051,343. However, in the couplers shown in these patents the saccharin group is in the coupling position, from which position it would be cleaved on coupling. In couplers of the present invention, the saccharin group is attached to a position from which it will not cleave as a result of coupling. Typically it forms part of the ballast group which renders the coupler and the dye formed from it nondiffusible in the layer in which it is coated.